The present invention generally relates to a method and apparatus for diagnosing a remaining lifetime of an aggregate constructed of a plurality of components, or parts wherein the remaining lifetimes of the components have a relationship with an entire remaining lifetime of the aggregate. More specifically, the present invention is directed to a remaining lifetime diagnostic method and a diagnostic apparatus thereof suitable for properly diagnosing the remaining lifetime of an aggregate, to a display method and a display apparatus for displaying a diagnosed result remaining lifetime and also to an expert system for inferring what measure is required based upon the acquired remaining lifetime.
Since parts or components for constructing an apparatus such as an electric power plant receive force externally applied thereto under higher temperatures, lifetime damage and degradation of materials occur when the parts have been utilized for a long time. Then, these components are required to be substituted by new components when a certain time period has elapsed. Accordingly, to predict such an exchanging time period of the components, remaining lifetimes thereof must be diagnosed. In the conventional cases, for example as described in JP-A-62-2 76470, the set lifetime values preset by the manufacturers when the apparatuses are manufactured, and also the predicted lifetime values acquired from the accelerated lifetime test data are utilized so as to diagnose the remaining lifetimes of the apparatuses. Furthermore, the degradation characteristic of the components, or parts for constructing the apparatus is obtained from the degradation characteristic test data, and the remaining lifetime of the apparatus is predicted based upon this degradation characteristic and the limit value of the parts. Moreover, the function test of the apparatus is performed so that the remaining lifetime of the apparatus is predicted based on the function test data.
There are problems in the above-described conventional techniques such that correct remaining lifetime can be hardly predicted for any of these apparatuses. For instance, in such a conventional method that the degradation characteristic of the components is acquired from the aging degradation characteristic test data and thus the remaining lifetime is predicted based upon this aging degradation characteristic, a large quantity of aging degradation characteristic test data on the parts or components are required so as to obtain a correct degradation chracteristic formula (it is required to destroy the parts for experimental purposes). This is caused by that the proper approximate equation for the degradation characteristic equation is not obtained.
Also, in another conventional method for predicting the remaining lifetime based upon the function test data of the apparatus while performing the periodrical maintenance, there are many apparatus the functions of which are not lowered during the inspection, and therefore prediction of the remaining lifetime must be realized by utilizing the experts experiences.
There are some possibilities that an apparatus which is not required for replacement is substituted by new one unless a remaining lifetime of this apparatus can be precisely predicted. It is not true that if an apparatus is new, there exists a few failure. However, an initial failure rate is greater than another failure rate of an apparatus under operation. As a consequence,. if a new apparatus is merely used for replacement without careful consideration, it causes higher cost and a safety problem may occur.
There is another problem in the conventional remaining lifetime diagnostic technique that no specific care is taken in readily representing the diagnosed results and a trend of an overall remaining lifetime to an operator.